Method and system for resolving addresses for network host interfaces from a cable modem

ABSTRACT

A method and system are provided to allow a cable modem to resolve addresses for a selected network host interface on a cable television network to connect the cable modem to a data network (e.g., the Internet). The cable modem is used in a data-over-cable system with telephony return. The cable modem is connected to a cable television network over a downstream cable data channel and connected to a public switched telephone network over a serial telephone line. The method provides a way for the cable modem to resolve an address for a selected network host interface (e.g., Internet Protocol host) available on the cable television system via the upstream channel connected to public switched telephone network. The method includes using existing Dynamic Host Configuration Protocol messages and message fields to discover network host interfaces available on the cable television system even though the cable modem only has downstream connection from the cable television network. The method and system can also be used on a data-over-cable system without telephony return.

FIELD OF INVENTION

The present invention relates to communications in computer networks. More specifically, it relates to a method and system for resolving addresses network host interfaces from a cable modem.

BACKGROUND OF THE INVENTION

Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta Ga., Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass., and others provide cable television services to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial ("HFC") cable system which have data rates of about 10 Mega-bits-per-second ("Mbps") to 30+ Mbps.

The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that requires a large bandwidth for downloading and viewing. Most Internet Service Providers ("ISPs") allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network ("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps to 30+ Mbps available on a coxial cable or HFC cable system on a cable television network.

With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks ("LANs") and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a "downstream" data rate of 30+ Mbps, which is a much larger data rate than can be supported by serial telephone line used over a modem.

However, most cable television networks provide only uni-directional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable system "headend" to a customer. A cable system headend is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. A return data path via a telephone network, such as a Public Switched Telephone Network provided by AT&T and others, (i.e., "telephony return") is typically used for an "upstream" data path. An upstream data path is the flow of data from the customer back to the cable system headend. A cable television system with an upstream connection to a telephony network is called a "data-over-cable system with telephony return."

An exemplary data-over-cable system with telephony return includes a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator, a cable modem, customer premise equipment (e.g., a customer computer) and a data network (e.g., the Internet). The cable modem termination system and the telephony remote access concentrator together are called a "telephony return termination system."

The cable modem termination system receives data packets from the data network and transmits them downstream via the cable television network to a cable modem attached to the customer premise equipment. The customer premise equipment sends responses data packets to the cable modem, which sends response data packets upstream via the public switched telephone network to the telephony remote access concentrator, which sends the response data packets back to the appropriate host on the data network. The data-over-cable system with telephony return provides transparent Internet Protocol ("IP") data traffic between customer premise equipment, a cable modem and the data network (e.g., the Internet or an intranet). As is known in the art, IP is a routing protocol designed to route traffic within a network or between networks.

When a cable modem used in the data-over-cable system with telephony return is initialized, it will make a connection to both the cable modem termination system via the cable network and to the telephony remote access concentrator via the public switched telephone network. If the cable modem is using telephony return, it will acquire telephony connection parameters on a downstream connection from the cable modem termination system and establish a Point-to-Point Protocol ("PPP") connection to connect an upstream channel to the telephony remote access concentrator. As is known in the art, PPP is used to encapsulate datagrams over a serial communications link. After a PPP connection is established, the cable modem negotiates a telephony IP address with the telephony remote access concentrator. The telephony IP address allows the customer premise equipment to send IP data packets upstream to the telephony remote access concentrator via the public switched telephone network to the data network.

The cable modem also needs to make an IP connection to the cable modem termination system so that IP data received on the cable modem termination system from the data network can be forwarded downstream to the customer premise equipment via the cable network and the cable modem. In one embodiment of the present invention, the cable modem establishes an IP address with the cable modem termination system through the telephony remote access concentrator using a Dynamic Host Configuration Protocol ("DHCP"). As is known in the art, DHCP provides configuration parameters for network host interfaces (e.g., IP interfaces) to network hosts.

There are several problems with using DHCP to configure network host interfaces such as IP interfaces available on the cable modem termination system. DHCP was not originally intended for use in configuring a system like the data-over-cable system with telephony return. In the data-over-cable system with telephony return, a cable modem desires to establish an IP connection with the data network with an IP interface available on the cable modem termination system. However, the cable modem only has a downstream connection from the cable modem termination system. The cable modem has an upstream connection to the telephony remote access concentrator via the public switched telephone network. However, the telephony remote access concentrator does not have any DHCP servers for receiving DHCP requests. The cable modem termination system has DHCP servers for receiving DHCP requests for network host interfaces, but it cannot be accessed directly by a cable modem in a data-over-cable system with telephony return.

The cable modem desires to create a DHCP-discover message, send it to the telephony remote access concentrator via the public switched telephone network and have the telephony remote access concentrator forward the message to a DHCP server associated with network host interfaces available on the cable modem termination system. However, there is currently no way to accomplish the connection scenario with DHCP since the telephony remote access concentrator has no mechanism to forward DHCP-discover messages to DHCP servers associated with the cable modem termination system. The DHCP servers are not directly addressable by a cable modem since the cable modem has only a downstream connection from the cable modem termination system via the cable network.

As a result, the cable modem cannot create a transparent IP data path using DHCP to receive IP data packets from the data network on a downstream data channel on the cable network from a network host interface available on the cable modem termination system and send IP data packet responses back to the data network upstream though the telephony remote access concentrator via the public switched telephone system.

The Motorola Corporation of Schaumburg, Ill., and others have proposed extensions to the DHCP protocol to solve the problems associated with using DHCP to configure data-over-cable systems with telephony return. However, the proposed extensions to DHCP require changes to the DHCP protocol specifically for the special case of a data-over-cable system with telephony return. This may not be desirable for the DHCP protocol, which was originally designed for other purposes. In addition, DHCP protocol extensions would require upgrading all existing DHCP servers on a large number of third party platforms. This would take a considerable amount of time and be very expensive to existing network owners. It is desirable to use the existing DHCP protocol to allow a transparent IP connection for a cable modem to/from a data network using a data-over-cable system with telephony return.

SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present invention, the problems associated with using the DHCP protocol to configure a data-over-cable system with telephony return are overcome. A method and system for resolving addresses for network interface hosts from a cable modem in a data-over-cable system with telephony return is provided.

A network host interface address is selected with the method and system described in co-pending application Ser. No. 09/018,784 assigned to the same assignee of the present application. The present invention resolves addresses for the selected network host interfaces.

The method and system include a first network device that is connected to a first network with a downstream connection of a first connection type, and connected to a second network with an upstream connection of a second connection type. The first and second networks are connected to a third network with a third connection type. In one embodiment of the present invention, the first network device is a cable modem, the first network is a cable television network, the second network is a public switched telephone network and the third network is a data network (e.g., the Internet). The downstream connection is a cable television connection, the upstream connection is a serial line connection, and the third connection is an IP connection.

The method includes receiving one or more first messages with a first message type on the first network device from the first network on the downstream connection. The one or more first messages are offers from one or more network host interfaces available on the first network to provide the first network device a connection to the third network. The first network device selects one of the network host interfaces using message fields in one of the one or more first messages. The first network device creates a second message with a second message type to accept the offered services from the selected network host interface. The second message includes a connection address for the first network in a first message field and an identifier to identify the selected network host interface in a second message field.

The first network device sends the second message over the upstream connection to the second network. The second network uses the second message field in the second message to forward the second message to the one or more network host interfaces available on first network. A network host interface available on the first network identified in second message field in the second message from the first network device recognizes its identifier in the second message field. The selected network host interface sends a third message with a third message type to the first network. The third message is an acknowledgment for the cable modem that the selected network host interface received the second message from the first network device. The first network stores a connection address for the selected network interface in one or more routing tables on the first network. The first network forwards the third message to the first network device. The first network and the first network device have the necessary addresses for a virtual connection that allows data to be sent from the third network to a network host interface on the first network, and from the first network over the downstream connection to the first network device.

In one embodiment of the present invention, the first, second and third messages and the first and second message fields are existing DHCP messages and DHCP message fields. The method accomplishes resolving network interface hosts addresses from a cable modem in a data-over-cable with telephony return without extensions to the existing DHCP protocol.

The method and system of the present invention are used in a data-over-cable system with telephony return. However, the present invention is not limited to a data-over-cable system with telephony return and can be used with a data-over-cable system without telephony return.

The foregoing and other features and advantages of an illustrative embodiment of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a cable modem system with telephony return;

FIG. 2 is a block diagram illustrating a protocol stack for a cable modem;

FIG. 3 is a block diagram illustrating a Telephony Channel Descriptor message structure;

FIG. 4 is a block diagram illustrating a Termination System Information message structure;

FIG. 5 is a flow diagram illustrating a method for addressing hosts in a cable modem system;

FIG. 6 is a block diagram illustrating a Dynamic Host Configuration Protocol message structure;

FIGS. 7A and 7B are a flow diagram illustrating a method for discovering hosts in a cable modem system;

FIG. 8 is a block diagram illustrating a data-over-cable system for the method illustrated in FIGS. 7A and 7B;

FIG. 9 is a block diagram illustrating the message flow of the method illustrated in FIGS. 7A and 7B;

FIGS. 10A and 10B are a flow diagram illustrating a method for resolving host addresses in a data-over-cable system;

FIG. 11 is a flow diagram illustrating a method for resolving discovered host addresses; and

FIG. 12 is a block diagram illustrating the message flow of the method illustrated in FIG. 10;

FIGS. 13A and 13B are a flow diagram illustrating a method for obtaining addresses for customer premise equipment;

FIGS. 14A and 14B are a flow diagram illustrating a method for resolving addresses for customer premise equipment;

FIGS. 15A and 15B are a flow diagram illustrating a method for addressing network host interfaces from customer premise equipment;

FIGS. 16A and 16B are a flow diagram illustrating a method for resolving network host interfaces from customer premise equipment; and

FIG. 17 is a block diagram illustrating a message flow for the methods in FIGS. 15A, 15B, and 16A and 16B.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Cable Modem System with Telephony Return

FIG. 1 is a block diagram illustrating a data-over-cable system with telephony return 10, hereinafter data-over-cable system 10. Most cable providers known in the art predominately provide uni-directional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable television network "headend" to customer premise equipment (e.g., a customer's personal computer). A cable television network headend is a central location that is responsible for sending cable signals in a downstream direction. A return path via a telephony network ("telephony return") is typically used for an "upstream" data path in uni-directional cable systems. An upstream data path is the flow of data from customer premise equipment back to the cable television network headend.

However, data-over-cable system 10 of the present invention may also provide a bi-directional data path (i.e., both downstream and upstream) without telephony return as is also illustrated in FIG. 1 and the present invention is not limited to a data-over-cable system with telephony return. In a data-over cable system without telephony return, customer premise equipment or cable modem has an upstream connection to the cable modem termination system via a cable television connection, a wireless connection, a satellite connection, or a connection via other technologies to send data upstream to the cable modem termination system.

Data-over-cable system 10 includes a Cable Modem Termination System ("CMTS") 12 connected to a cable television network 14, hereinafter cable network 14. Cable network 14 includes cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications, or Atlanta, Ga., Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, of Marietta, Ga., Continental Cablevision, Inc., of Boston, Mass., and others. Cable network 14 is connected to a Cable Modem ("CM") 16 with a downstream cable connection.

CM 16 is connected to Customer Premise Equipment ("CPE") 18 such as a personal computer system via a Cable Modem-to-CPE Interface ("CMCI") 20. CM 16 is connected to a Public Switched Telephone Network ("PSTN") 22 with an upstream telephony connection. PSTN 22 includes those public switched telephone networks provided by AT&T, Regional Bell Operating Companies (e.g., Ameritch, U.S. West, Bell Atlantic, Southern Bell Communications, Bell South, NYNEX, and Pacific Telesis Group), GTE, and others. The upstream telephony connection is any of a standard telephone line connection, Integrated Services Digital Network ("ISDN") connection, Asymmetric Digital Subscriber Line ("ADSL") connection, or other telephony connection. PSTN 22 is connected to a Telephony Remote Access Concentrator ("TRAC") 24. In a data-over cable system without telephony return, CM 16 has an upstream connection to CMTS 12 via a cable television connection, a wireless connection, a satellite connection, or a connection via other technologies to send data upstream outside of the telephony return path. An upstream cable television connection via cable network 14 is illustrated in FIG. 1.

FIG. 1 illustrates a telephony modem integral to CM 16. In another embodiment of the present invention, the telephony modem is a separate modem unit external to CM 16 used specifically for connecting with PSTN 22. A separate telephony modem includes a connection to CM 16 for exchanging data. CM 16 includes cable modems provided by the 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others. In yet another embodiment of the present invention, CM 16 includes functionality to connect only to cable network 14 and receives downstream signals from cable network 14 and sends upstream signals to cable network 14 without telephony return. The present invention is not limited to cable modems used with telephony return.

CMTS 12 and TRAC 24 may be at a "headend" of cable system 10, or TRAC 24 may be located elsewhere and have routing associations to CMTS 12. CMTS 12 and TRAC 24 together are called a "Telephony Return Termination System" ("TRTS") 26. TRTS 26 is illustrated by a dashed box in FIG. 1. CMTS 12 and TRAC 24 make up TRTS 26 whether or not they are located at the headend of cable network 14, and TRAC 24 may in located in a different geographic location from CMTS 12. Content severs, operations servers, administrative servers and maintenance servers used in data-over-cable system 10 (not shown in FIG. 1) may also be in different locations. Access points to data-over-cable system 10 are connected to one or more CMTS's 12 or cable headend access points. Such configurations may be "one-to-one", "one-to-many," or "many-to-many," and may be interconnected to other Local Area Networks ("LANs") or Wide Area Networks ("WANs").

TRAC 24 is connected to a data network 28 (e.g., the Internet or an intranet) by a TRAC-Network System Interface 30 ("TRAC-NSI"). CMTS 12 is connected to data network 28 by a CMTS-Network System Interface ("CMTS-NSI") 32. The present invention is not limited to data-over-cable system 10 illustrated in FIG. 1, and more or fewer components, connections and interfaces could also be used.

Cable Modem Protocol Stack

FIG. 2 is a block diagram illustrating a protocol stack 36 for CM 16. FIG. 2 illustrates the downstream and upstream protocols used in CM 16. As is known in the art, the Open System Interconnection ("OSI") model is used to describe computer networks. The OSI model consists of seven layers including from lowest-to-highest, a physical, data-link, network, transport, session, application and presentation layer. The physical layer transmits bits over a communication link. The data link layer transmits error free frames of data. The network layer transmits and routes data packets.

For downstream data transmission, CM 16 is connected to cable network 14 in a physical layer 38 via a Radio Frequency ("RF") Interface 40. In an illustrative embodiment of the present invention, RF Interface 40 has an operation frequency range of 50 Mega-Hertz ("MHz") to 1 Giga-Hertz ("GHz") and a channel bandwidth of 6 MHz. However, other operation frequencies may also be used and the invention is not limited to these frequencies. RF interface 40 uses a signal modulation method of Quadrature Amplitude Modulation ("QAM"). As is known in the art, QAM is used as a means of encoding digital information over radio, wire, or fiber optic transmission links. QAM is a combination of amplitude and phase modulation and is an extension of multiphase phase-shift-keying. QAM can have any number of discrete digital levels typically including 4, 16, 64 or 256 levels. In one embodiment of the present invention, QAM-64 is used in RF interface 40. However, other operating frequencies modulation methods could also be used. For more information on RF interface 40 see the Institute of Electrical and Electronic Engineers ("IEEE") standard 802.14 for cable modems incorporated herein by reference. IEEE standards can be found on the World Wide Web at the Universal Resource Locator ("URL") "www.ieee.org." However, other RF interfaces 40 could also be used and the present invention is not limited to IEEE 802.14 (e.g., RF interfaces from Multimedia Cable Network Systems ("MCNS") and others can also be used).

Above RF interface 40 in a data-link layer 42 is a Medium Access Control ("MAC") layer 44. As is known in the art, MAC layer 44 controls access to a transmission medium via physical layer 38. For more information on MAC layer protocol 44 see IEEE 802.14 for cable modems. However, other MAC layer protocols 44 could also be used and the present invention is not limited to IEEE 802.14 MAC layer protocols (e.g., MCNS MAC layer protocols and others could also be used).

Above MAC layer 44 is an optional link security protocol stack 46. Link security protocol stack 46 prevents authorized users from making a data connection from cable network 14. RF interface 40 and MAC layer 44 can also be used for an upstream connection if data-over-cable system 10 is used without telephony return.

For upstream data transmission with telephony return, CM 16 is connected to PSTN 22 in physical layer 38 via modem interface 48. The International Telecommunications Union-Telecommunication Standardization Sector ("ITU-T", formerly known as the CCITT) defines standards for communication devices identified by "V.xx" series where "xx" is an identifying number. ITU-T standards can be found on the World Wide Web at the URL "www.itu.ch."

In one embodiment of the present invention, ITU-T V.34 is used as modem interface 48. As is known in the art, ITU-T V.34 is commonly used in the data link layer for modem communications and currently allows data rates as high as 33,600 bits-per-second ("bps"). For more information see the ITU-T V.34 standard. However, other modem interfaces or other telephony interfaces could also be used.

Above modem interface 48 in data link layer 42 is Point-to-Point Protocol ("PPP") layer 50, hereinafter PPP 50. As is known in the art, PPP is used to encapsulate network layer datagrams over a serial communications link. For more information on PPP see Internet Engineering Task Force ("IETF") Request for Comments ("RFC"), RFC-1661, RFC-1662 and RFC-1663 incorporated herein by reference. Information for IETF RFCs can be found on the World Wide Web at URLs "ds.internic.net" or "www.ietf.org."

Above both the downstream and upstream protocol layers in a network layer 52 is an Internet Protocol ("IP") layer 54. IP layer 54, hereinafter IP 54, roughly corresponds to OSI layer 3, the network layer, but is typically not defined as part of the OSI model. As is known in the art, IP 54 is a routing protocol designed to route traffic within a network or between networks. For more information on IP 54 see RFC-791 incorporated herein by reference.

Internet Control Message Protocol ("ICMP") layer 56 is used for network management. The main functions of ICMP layer 56, hereinafter ICMP 56, include error reporting, reachability testing (e.g., "pinging") congestion control, route-change notification, performance, subnet addressing and others. Since IP 54 is an unacknowledged protocol, datagrams may be discarded and ICMP 56 is used for error reporting. For more information on ICMP 56 see RFC-971 incorporated herein by reference.

Above IP 54 and ICMP 56 is a transport layer 58 with User Datagram Protocol layer 60 ("UDP"). UDP layer 60, hereinafter UDP 60, roughly corresponds to OSI layer 4, the transport layer, but is typically not defined as part of the OSI model. As is known in the art, UDP 60 provides a connectionless mode of communications with datagrams. For more information on UDP 60 see RFC-768 incorporated herein by reference.

Above the network layer are a Simple Network Management Protocol ("SNMP") layer 62, Trivial File Protocol ("TFTP") layer 64, Dynamic Host Configuration Protocol ("DHCP") layer 66 and a UDP manager 68. SNMP layer 62 is used to support network management functions. For more information on SNMP layer 62 see RFC-1157 incorporated herein by reference. TFTP layer 64 is a file transfer protocol used to download files and configuration information. For more information on TFTP layer 64 see RFC-1350 incorporated herein by reference. DHCP layer 66 is a protocol for passing configuration information to hosts on an IP 54 network. For more information on DHCP layer 66 see RFC-1541 incorporated herein by reference. UDP manager 68 distinguishes and routes packets to an appropriate service (e.g., a virtual tunnel). More or few protocol layers could also be used with data-over-cable system 10.

CM 16 supports transmission and reception of IP 54 datagrams as specified by RFC-791. CMTS 12 and TRAC 24 may perform filtering of IP 54 datagrams. CM 16 is configurable for IP 54 datagram filtering to restrict CM 16 and CPE 18 to the use of only their assigned IP 54 addresses. CM 16 is configurable for IP 54 datagram UDP 60 port filtering (i.e., deep filtering).

CM 16 forwards IP 54 datagrams destined to an IP 54 unicast address across cable network 14 or PSTN 22. Some routers have security features intended to filter out invalid users who alter or masquerade packets as if sent from a valid user. Since routing policy is under the control of network operators, such filtering is a vendor specific implementation. For example, dedicated interfaces (i.e., Frame Relay) may exist between TRAC 24 and CMTS 12 which preclude filtering, or various forms of virtual tunneling and reverse virtual tunneling could be used to virtually source upstream packets from CM 16. For more information on virtual tunneling see Level 2 Tunneling Protocol ("L2TP") or Point-to-Point Tunneling Protocol ("PPTP") in IETF draft documents incorporated herein by reference by Kory Hamzeh, et. al (IETF draft documents are precursors to IETF RFCs and are works in progress).

CM 16 also forwards IP 54 datagrams destined to an IP 54 multicast address across cable network 14 or PSTN 22. CM 16 is configurable to keep IP 54 multicast routing tables and to use group membership protocols. CM 16 is also capable of IP 54 tunneling upstream through the telephony path. A CM 16 that wants to send a multicast packet across a virtual tunnel will prepend another IP 54 header, set the destination address in the new header to be the unicast address of CMTS 12 at the other end of the tunnel, and set the IP 54 protocol field to be four, which means the next protocol is IP 54.

CMTS 12 at the other end of the virtual tunnel receives the packet, strips off the encapsulating IP 54 header, and forwards the packet as appropriate. A broadcast IP 54 capability is dependent upon the configuration of the direct linkage, if any, between TRAC 24 and CMTS 12. CMTS 12, CM 16, and TRAC 24 are capable of routing IP 54 datagrams destined to an IP 54 broadcast address which is across cable network 14 or PSTN 22 if so configured. CM 16 is configurable for IP 54 broadcast datagram filtering.

An operating environment for CM 16 of the present invention includes a processing system with at least one high speed Central Processing Unit ("CPU") and a memory system. In accordance with the practices of persons skilled in the art of computer programming, the present invention is described below with reference to acts and symbolic representations of operations that are performed by the processing system, unless indicated otherwise. Such acts and operations are sometimes referred to as being "computer-executed", or "CPU executed."

It will be appreciated that the acts and symbolically represented operations include the manipulation of electrical signals by the CPU. The electrical system represent data bits which cause a resulting transformation or reduction of the electrical signal representation, and the maintenance of data bits at memory locations in the memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to the data bits.

The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, organic disks, and any other volatile or non-volatile mass storage system readable by the CPU. The computer readable medium includes cooperating or interconnected computer readable media, which exist exclusively on the processing system or is distributed among multiple interconnected processing systems that may be local or remote to the processing system.

Initialization of a Cable Modem with Telephony Return

When CM 16 is initially powered on, if telephony return is being used, CM 16 will receive a Telephony Channel Descriptor ("TCD") from CMTS 12 that is used to provide dialing and access instructions on downstream channels via cable network 14. Information in the TCD is used by CM 16 to connect to TRAC 24. The TCD is transmitted as a MAC management message with a management type value of TRI₋₋ TCD at a periodic interval (e.g., every 2 seconds). To provide for flexibility, the TCD message parameters are encoded in a Type/Length/Value ("TLV") form. However, other encoding techniques could also be used. FIG. 3 is a block diagram illustrating a TCD message structure 70 with MAC 44 management header 72 and Service Provider Descriptor(s) ("SPD") 74 encoded in TLV format. SPDs 74 are compound TLV encodings that define telephony physical-layer characteristics that are used by CM 16 to initiate a telephone call. SPD 74 is a TLV-encoded data structure that contains sets of dialing and access parameters for CM 16 with telephony return. SPD 74 is contained within TCD message 70. There may be multiple SPD 74 encodings within a single TCD message 70. There is at least one SPD 74 in TCD message 70. SPD 74 parameters are encoded as SPD-TLV tuples. SPD 74 contains the parameters shown in Table 1 and may contain optional vendor specific parameters. However, more or fewer parameters could also be used in SPD 74.

                  TABLE 1                                                          ______________________________________                                         SPD 74 Parameter                                                                              Description                                                     ______________________________________                                         Factory Default Flag                                                                          Boolean value, if TRUE(1), indicates a                                         SPD which should be used by CM 16.                              Service Provider Name                                                                         This parameter includes the name of a                                          service provider. Format is standard                                           ASCII string composed of numbers and                                           letters.                                                        Telephone Numbers                                                                             These parameters contain telephone                                             numbers that CM 16 uses to initiate a                                          telephony modem link during a login                                            process. Connections are attempted in                                          ascending numeric order (i.e., Phone                                           Number 1, Phone Number 2...). The SPD                                          contains a valid telephony dial string as                                      the primary dial string (Phone Number 1),                                      secondary dial-strings are optional.                                           Format is ASCII string(s) composed of:                                         any sequence of numbers, pound "#" and                                         star "*" keys and comma character ","                                          used to indicate a two second pause in                                         dialing.                                                        Connection Threshold                                                                          The number of sequential connection                                            failures before indicating connection                                          failure. A dial attempt that does not result                                   in an answer and connection after no                                           more than ten rings is considered a                                            failure. The default value is one.                              Login User Name                                                                               This contains a user name CM 16 will use                                       an authentication protocol over the                                            telephone link during the initialization                                       procedure. Format is a monolithic                                              sequence of alphanumeric characters in                                         an ASCII string composed of numbers                                            and letters.                                                    Login Password This contains a password that CM 16 will                                       use during authentication over a                                               telephone link during the initialization                                       procedure. Format is a monolithic                                              sequence of alphanumeric characters in                                         an ASCII string composed of numbers                                            and letters.                                                    DHCP Authenticate                                                                             Boolean value, reserved to indicate that                                       CM 16 uses a specific indicated DHCP 66                                        Server (see next parameter) for a DHCP                                         66 Client and BOOTP Relay Process                                              when TRUE (one). The default is FALSE                                          (zero) which allows any DHCP 66 Server.                         DHCP Server    IP 54 address value of a DHCP 66 Server                                        CM 16 uses for DHCP 66 Client and                                              BOOTP Relay Process. If this attribute is                                      present and DHCP 66 Authenticate                                               attribute is TRUE(1). The default value is                                     integer zero.                                                   RADIUS Realm   The realm name is a string that defines a                                      RADIUS server domain. Format is a                                              monolithic sequence of alphanumeric                                            characters in an ACSII string composed                                         of numbers and letters.                                         PPP Authentication                                                                            This parameter instructs the telephone                                         modem which authentication procedure to                                        perform over the telephone link.                                Demand Dial Timer                                                                             This parameter indicates time (in                                              seconds) of inactive networking time that                                      will be allowed to elapse before hanging                                       up a telephone connection at CM 16. If                                         this optional parameter is not present, or                                     set to zero, then the demand dial feature                                      is not activated. The default value is zero.                    Vendor Specific Extensions                                                                    Optional vendor specific extensions.                            ______________________________________                                    

A Termination System Information ("TSI") message is transmitted by CMTS 12 at periodic intervals (e.g., every 2 seconds) to report CMTS 12 information to CM 16 whether or not telephony return is used. The TSI message is transmitted as a MAC 44 management message. The TSI provides a CMTS 12 boot record in a downstream channel to CM 16 via cable network 14. Information in the TSI is used by CM 16 to obtain information about the status of CMTS 12. The TSI message has a MAC 44 management type value of TRI₋₋ TSI.

FIG. 4 is a block diagram of a TSI message structure 76. TSI message structure 76 includes a MAC 44 management header 78, a downstream channel IP address 80, a registration IP address 82, a CMTS 12 boot time 84, a downstream channel identifier 86, an epoch time 88 and vendor specific TLV encoded data 90.

A description of the fields of TSI message 76 are shown in Table 2. However, more or fewer fields could also be used in TSI message 76.

                  TABLE 2                                                          ______________________________________                                         TSI 76 Parameter                                                                               Description                                                    ______________________________________                                         Downstream Channel                                                                             This field contains an IP 54 address of                        IP Address 80   CMTS 12 available on the downstream                                            channel this message arrived on.                               Registration IP Address 82                                                                     This field contains an IP 54 address                                           CM 16 sends its registration request                                           messages to. This address MAY be                                               the same as the Downstream Channel                                             IP 54 address.                                                 CMTS Boot Time 84                                                                              Specifies an absolute-time of a CMTS                                           12 recorded epoch. The clock setting                                           for this epoch uses the current clock                                          time with an unspecified accuracy.                                             Time is represented as a 32 bit binary                                         number.                                                        Downstream Channel ID 86                                                                       A downstream channel on which this                                             message has been transmitted. This                                             identifier is arbitrarily chosen by CMTS                                       12 and is unique within the MAC 44                                             layer.                                                         Epoch 88        An integer value that is incremented                                           each time CMTS 12 is either re-                                                initialized or performs address or                                             routing table flush.                                           Vendor Specific Extensions 90                                                                  Optional vendor extensions may be                                              added as TLV encoded data.                                     ______________________________________                                    

After receiving TCD 70 message and TSI message 76, CM 16 continues to establish access to data network 28 (and resources on the network) by first dialing into TRAC 24 and establishing a telephony PPP 50 session. Upon the completion of a successful PPP 50 connection, CM 16 performs PPP Link Control Protocol ("LCP") negotiation with TRAC 24. Once LCP negotiation is complete, CM 16 requests Internet Protocol Control Protocol ("IPCP") address negotiation. For more information on IPCP see RFC-1332 incorporated herein by reference. During IPCP negotiation, CM 16 negotiates an IP 54 address with TRAC 24 for sending IP 54 data packet responses back to data network 28 via TRAC 24.

When CM 16 has established an IP 54 link to TRAC 24, it begins "upstream" communications to CMTS 12 via DHCP layer 66 to complete a virtual data connection by attempting to discover network host interfaces available on CMTS 12 (e.g., IP 54 host interfaces for a virtual IP 54 connection). The virtual data connection allows CM 16 to receive data from data network 28 via CMTS 12 and cable network 14, and send return data to data network 28 via TRAC 24 and PSTN 22. CM 16 must first determine an address of a host interface (e.g., an IP 54 interface) available on CMTS 12 that can be used by data network 28 to send data to CM 16. However, CM 16 has only a downstream connection from CMTS 12 and has to obtain a connection address to data network 28 using an upstream connection to TRAC 24.

Addressing Network Host Interfaces in the Data-over-cable System Via the Cable Modem

FIG. 5 is a flow diagram illustrating a method 92 for addressing network host interfaces in a data-over-cable system with telephony return via a cable modem. Method 92 allows a cable modem to establish a virtual data connection to a data network. In method 92, multiple network devices are connected to a first network with a downstream connection of a first connection type, and connected to a second network with an upstream connection of a second connection type. The first and second networks are connected to a third network with a third connection type.

At step 94, a selection input is received on a first network device from the first network over the downstream connection. The selection input includes a first connection address allowing the first network device to communicate with the first network via upstream connection to the second network. At step 96, a first message of a first type for a first protocol is created on the first network device having the first connection address from the selection input in a first message field. The first message is used to request a network host interface address on the first network. The first connection address allows the first network device to have the first message with the first message type forwarded to network host interfaces available on the first network via the upstream connection to the second network.

At step 98, the first network device sends the first message over the upstream connection to the second network. The second network uses the first address field in the first message to forward the first message to one or more network host interfaces available on first network at step 100. Network host interfaces available on the first network that can provide the services requested in first message send a second message with a second message type with a second connection address in a second message field to the first network at step 102. The second connection address allows the first network device to receive data packets from the third network via a network host interface available on the first network. The first network forwards one or more second messages on the downstream connection to the first network device at step 104.

The first network device selects a second connection address from one of the second messages from one of the one or more network host interfaces available on the first network at step 106 and establishes a virtual connection from the third network to the first network device using the second connection address for the selected network host interface.

The virtual connection includes receiving data on the first network host interface on the first network from the third network and sending the data over the downstream connection to the first network device. The first network device sends data responses back to the third network over the upstream connection to the second network, which forwards the data to the appropriate destination on the third network.

In one embodiment of the present invention, the data-over-cable system is data-over-cable system 10, the first network device is CM 16, the first network is cable television network 14, the downstream connection is a cable television connection. The second network is PSTN 22, the upstream connection is a telephony connection, the third network is data network 28 (e.g., the Internet or an intranet) and the third type of connection is an IP 54 connection. The first and second connection addresses are IP 54 addresses. However, the present invention is not limited to the network components and addresses described. Method 92 allows CM 16 to determine an IP 54 network host interface address available on CMTS 12 to receive IP 54 data packets from data network 28, thereby establishing a virtual IP 54 connection with data network 28.

After addressing network host interfaces using method 92, an exemplary data path through cable system 10 is illustrated in Table 3. However other data paths could also be used and the present invention is not limited to the data paths shown in Table 3. For example, CM 16 may send data upstream back through cable network 14 (e.g., CM 16 to cable network 14 to CMTS 12) and not use PSTN 22 and the telephony return upstream path.

                  TABLE 3                                                          ______________________________________                                         1.  An IP 54 datagram from data network 28 destined for CM 16 arrives              on CMTS-NSI 32 and enters CMTS 12.                                         2.  CMTS 12 encodes the IP 54 datagram in a cable data frame, passes it            to MAC 44 and transmits it "downstream" to RF interface 40 on                  CM 16 via cable network 14.                                                3.  CM 16 recognizes the encoded IP 54 datagram in MAC layer 44                    received via RF interface 40.                                              4.  CM 16 responds to the cable data frame and encapsulates a response             IP 54 datagram in a PPP 50 frame and transmits it "upstream" with              modem interface 48 via PSTN 22 to TRAC 24.                                 5.  TRAC 24 decodes the IP 54 datagram and forwards it via                         TRAC-NSI 30 to a destination on data network 28.                           ______________________________________                                    

Dynamic Network Host Configuration on Data-over-cable System

As was illustrated in FIG. 2, CM 16 includes a Dynamic Host Configuration Protocol ("DHCP") layer 66, hereinafter DHCP 66. DHCP 66 is used to provide configuration parameters to hosts on a network (e.g., an IP 54 network). DHCP 66 consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP 66 server to a host and a mechanism for allocation of network host addresses to hosts. DHCP 66 is built on a client-server model, where designated DHCP 66 servers allocate network host addresses and deliver configuration parameters to dynamically configured network host clients.

FIG. 6 is a block diagram illustrating a DHCP 66 message structure 108. The format of DHCP 66 messages is based on the format of BOOTstrap Protocol ("BOOTP") messages described in RFC-951 and RFC-1542 incorporated herein by reference. From a network host client's point of view, DHCP 66 is an extension of the BOOTP mechanism. This behavior allows existing BOOTP clients to interoperate with DHCP 66 servers without requiring any change to network host the clients' BOOTP initialization software. DHCP 66 provides persistent storage of network parameters for network host clients.

To capture BOOTP relay agent behavior described as part of the BOOTP specification and to allow interoperability of existing BOOTP clients with DHCP 66 servers, DHCP 66 uses a BOOTP message format. Using BOOTP relaying agents eliminates the necessity of having a DHCP 66 server on each physical network segment.

DHCP 66 message structure 108 includes an operation code field 110 ("op"), a hardware address type field 112 ("htype"), a hardware address length field 114 ("hlen"), a number of hops field 116 ("hops"), a transaction identifier field 118 ("xid"), a seconds elapsed time field 120 ("secs"), a flags field 122 ("flags"), a client IP address field 124 ("ciaddr"), a your IP address field 126 ("yiaddr"), a server IP address field 128 ("siaddr"), a gateway/relay agent IP address field 130 ("giaddr"), a client hardware address field 132 ("chaddr"), an optional server name field 134 ("sname"), a boot file name 136 ("file") and an optional parameters field 138 ("options"). Descriptions for DHCP 66 message 108 fields are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         DCHP 66                                                                        Parameter    Description                                                       ______________________________________                                         OP 110       Message op code / message type.                                                1 BOOTREQUEST, 2 = BOOTREPLY.                                     HTYPE 112    Hardware address type (e.g., `1` = 10                                          Mps Ethernet).                                                    HLEN 114     Hardware address length (e.g. `6` for 10                                       Mbps Ethernet).                                                   HOPS 116     Client sets to zero, optionally used by                                        relay-agents when booting via a relay-                                         agent.                                                            XID 118      Transaction ID, a random number                                                chosen by the client, used by the client                                       and server to associate messages and                                           responses between a client and a                                               server.                                                           SECS 120     Filled in by client, seconds elapsed                                           since client started trying to boot.                              FLAGS 122    Flags including a BROADCAST bit.                                  CIADDR 124   Client IP address; filled in by client in                                      DHCPREQUEST if verifying previously                                            allocated configuration parameters.                               YIADDR 126   `Your` (client) IP address.                                       SIADDR 128   IP 54 address of next server to use in                                         bootstrap; returned in DHCPOFFER,                                              DHCPACK and DHCPNAK by server.                                    GIADDR 130   Gateway relay agent IP 54 address,                                             used in booting via a relay-agent.                                CHADDR       Client hardware address (e.g., MAC                                132          layer 44 address).                                                SNAME 134    Optional server host name, null                                                terminated string.                                                FILE 136     Boot file name, terminated by a null                                           string.                                                           OPTIONS      Optional parameters.                                              138                                                                            ______________________________________                                    

The DHCP 66 message structure shown in FIG. 6 is used to discover IP 54 and other network host interfaces in data-over-cable system 10. A network host client (e.g., CM 16) uses DHCP 66 to acquire or verify an IP 54 address and network parameters whenever the network parameters may have changed. Table 5 illustrates a typical use of the DHCP 66 protocol to discover a network host interface from a network host client.

                  TABLE 5                                                          ______________________________________                                         1.  A network host client broadcasts a DHCP 66 discover message on its             local physical subnet. The DHCP 66 discover message may include                options that suggest values for a network host interface address.              BOOTP relay agents may pass the message on to DHCP 66 servers                  not on the same physical subnet.                                           2.  DHCP servers may respond with a DHCPOFFER message that                         includes an available network address in the `yiaddr` field (and               other configuration parameters in DHCP 66 options) from a network              host interface. DHCP 66 servers unicasts the DHCPOFFER message                 to the network host client (using the DHCP/BOOTP relay agent if                necessary) if possible, or may broadcast the message to a broadcast            address (preferably 255.255.255.255) on the client's subnet.               3.  The network host client receives one or more DHCPOFFER messages                from one or more DHCP 66 servers. The network host client may                  choose to wait for multiple responses.                                     4.  The network host client chooses one DHCP 66 server with an                     associated network host interface from which to request                        configuration                                                                  parameters, based on the configuration parameters offered in the               DHCPOFFER messages.                                                        ______________________________________                                    

Discovering Network Host Interfaces in the Data-over-cable System

The DHCP discovery process illustrated in table 5 will not work in data-over-cable system 10. CM 16 has only a downstream connection from CMTS 12, which includes DHCP 66 servers, associated with network host interfaces available on CMTS 12. In an illustrative embodiment of the present invention, CM 16 discovers network host interfaces via TRAC 24 and PSTN 22 on an upstream connection.

The DHCP 66 addressing process shown in Table 5 was not originally intended to discover network host interfaces in data-over-cable system 10. CMTS 12 has DHCP 66 servers associated with network host interfaces (e.g., IP interfaces), but CM 16 only has as downstream connection from CMTS 12. CM 16 has an upstream connection to TRAC 24, which has a DHCP 66 layer. However, TRAC 24 does not have DHCP 66 servers, or direct access to network host interfaces on CMTS 12.

FIGS. 7A and 7B are a flow diagram illustrating a method 140 for discovering network host interfaces in data-over-cable system 10. When CM 16 has established an IP 54 link to TRAC 24, it begins communications with CMTS 12 via DHCP 66 to complete a virtual IP 54 connection with data network 28. However, to discover what IP 54 host interfaces might be available on CMTS 12, CM 16 has to communicate with CMTS 12 via PSTN 22 and TRAC 24 since CM 16 only has a "downstream" cable channel from CMTS 12.

At step 142 in FIG. 7A, after receiving a TSI message 76 from CMTS 12 on a downstream connection, CM 16 generates a DHCP discover ("DHCPDISCOVER") message and sends it upstream via PSTN 22 to TRAC 22 to discover what IP 54 interfaces are available on CMTS 12. The fields of the DHCP discover message are set as illustrated in Table 6. However, other field settings may also be used.

                  TABLE 6                                                          ______________________________________                                         DHCP 66                                                                        Parameter   Description                                                        ______________________________________                                         OP 110      Set to BOOTREQUEST.                                                HTYPE 112   Set to network type (e.g., one for 10 Mbps                                     Ethernet).                                                         HLEN 114    Set to network length (e.g., six for 10 Mbps                                   Ethernet)                                                          HOPS 116    Set to zero.                                                       FLAGS 118   Set BROADCAST bit to zero.                                         CIADDR 124  If CM 16 has previously been assigned an IP                                    54 address, the IP 54 address is placed in this                                field. If CM 16 has previously been assigned                                   an IP 54 address by DHCP 66, and also has                                      been assigned an address via IPCP, CM 16                                       places the DHCP 66 IP 54 address in this                                       field.                                                             GIADDR 130  CM 16 places the Downstream Channel IP 54                                      address 80 of CMTS 12 obtained in TSI                                          message 76 on a cable downstream channel                                       in this field.                                                     CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                     in this field.                                                     ______________________________________                                    

The DHCPDISCOVER message is used to "discover" the existence of one or more IP 54 host interfaces available on CMTS 12. DHCP 66 giaddr-field 130 (FIG. 6) includes the downstream channel IP address 80 of CMTS 12 obtained in TSI message 76 (e.g., the first message field from step 96 of method 92). Using the downstream channel IP address 80 of CMTS 12 obtained in TSI message 76 allows the DHCPDISCOVER message to be forwarded by TRAC 24 to DHCP 66 servers (i.e., protocol servers) associated with network host interfaces available on CMTS 12. If DHCP 66 giaddr-field 130 (FIG. 6) in a DHCP message from a DHCP 66 client is non-zero, the DHCP 66 server sends any return messages to a DHCP 66 server port on a DHCP 66 relaying agent (e.g., CMTS 12) whose address appears in DHCP 66 giaddr-field 130.

In a typical DHCP 66 discovery process the DHCP 66 giaddr-field 130 is set to zero. If DHCP 66 giaddr-field 130 is zero, the DHCP 66 client is on the same subnet as the DHCP 66 server, and the DHCP 66 server sends any return messages to either the DHCP 66 client's network address, if that address was supplied in DHCP 66 ciaddr-field 124 (FIG. 6), or to a client's hardware address specified in DHCP 66 chaddr-field 132 (FIG. 6) or to a local subnet broadcast address (e.g., 255.255.255.255).

At step 144, a DHCP 66 layer on TRAC 24 broadcasts the DHCPDISCOVER message on its local network leaving DHCP 66 giaddr-field 130 intact since it already contains a non-zero value. TRAC's 24 local network includes connections to one or more DHCP 66 proxies (i.e., network host interface proxies). The DHCP 66 proxies accept DHCP 66 messages originally from CM 16 destined for DHCP 66 servers connected to network host interfaces available on CMTS 12 since TRAC 24 has no direct access to DCHP 66 servers associated with network host interfaces available on CMTS 12. DHCP 66 proxies are not used in a typical DHCP 66 discovery process.

One or more DHCP 66 proxies on TRAC's 24 local network recognizes the DHCPDISCOVER message and forwards it to one or more DHCP 66 servers associated with network host interfaces (e.g., IP 54 interfaces) available on CMTS 12 at step 146. Since DHCP 66 giaddr-field 130 (FIG. 6) in the DHCPDISCOVER message sent by CM 16 is already non-zero (i.e., contains the downstream IP address of CMTS 12), the DHCP 66 proxies also leave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for network host interfaces (e.g., IP 54 interfaces) available on CMTS 12 receive the DHCPDISCOVER message and generate a DHCP 66 offer message ("DHCPOFFER") at step 148. The DHCP 66 offer message is an offer of configuration parameters sent from network host interfaces to DHCP 66 servers and back to a network host client (e.g., CM 16) in response to a DHCPDISCOVER message. The DHCP 66 offer message is sent with the message fields set as illustrated in Table 7. However, other field settings can also be used. DHCP 66 yiaddr-field 126 (e.g., second message field from step 102 of method 92) contains an IP 54 address for a network host interface available on CMTS 12 and used for receiving data packets from data network 28.

                  TABLE 7                                                          ______________________________________                                         DHCP 66 Parameter                                                                              Description                                                    ______________________________________                                         FLAGS 122       BROADCAST bit set to zero.                                     YIADDR 126      IP 54 address from a network                                                   host interface to allow CM 16 to                                               receive data from data network                                                 28 via a network host interface                                                available on CMTS 12.                                          SIADDR 128      An IP 54 address for a TFTP 64                                                 server to download configuration                                               information for an interface host.                             CHADDR 132      MAC 44 address of CM 16.                                       SNAME 134       Optional DHCP 66 server                                                        identifier with an interface host.                             FILE 136        A TFTP 64 configuration file                                                   name for CM 16.                                                ______________________________________                                    

DHCP 66 servers send the DHCPOFFER message to the address specified in 66 giaddr-field 130 (i.e., CMTS 12) from the DHCPDISCOVER message if associated network host interfaces (e.g., IP 54 interfaces) can offer the requested service (e.g., IP 54 service) to CM 16. The DHCPDISOVER message DHCP 66 giaddr-field 130 contains a downstream channel IP address 80 of CMTS 12 that was received by CM 16 in TSI message 76. This allows CMTS 12 to receive the DHCPOFFER messages from the DHCP 66 servers and send them to CM 16 via a downstream channel on cable network 14.

At step 150 in FIG. 7B, CMTS 12 receives one or more DHCPOFFER messages from one or more DHCP 66 servers associated with the network host interfaces (e.g., IP 54 interfaces). CMTS 12 examines DHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messages and sends the DHCPOFFER messages to CM 16 via cable network 14. DHCP 66 yiaddr-field 126 contains an IP 54 address for a network host IP 54 interface available on CMTS 12 and used for receiving IP 54 data packets from data network 28. DHCP 66 chaddr-field 132 contains the MAC 44 layer address for CM 16 on a downstream cable channel from CMTS 12 via cable network 14. CMTS 12 knows the location of CM 16 since it sent CM 16 a MAC 44 layer address in one or more initialization messages (e.g., TSI message 76).

If a BROADCAST bit in flags field 124 is set to one, CMTS 12 sends the DHCPOFFER messages to a broadcast IP 54 address (e.g., 255.255.255.255) instead of the address specified in DHCP 66 yiaddr-field 126. DHCP 66 chaddr-field 132 is still used to determine that MAC 44 layer address. If the BROADCAST bit in DHCP 66 flags field 122 is set, CMTS 12 does not update internal address or routing tables based upon DHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when a broadcast message is sent.

At step 152, CM 16 receives one or more DHCPOFFER messages from CMTS 12 via cable network 14 on a downstream connection. At step 154, CM 16 selects an offer for IP 54 service from one of the network host interfaces (e.g., an IP interfaces 54) available on CMTS 12 that responded to the DHCPDISOVER message sent at step 142 in FIG. 7A and establishes a virtual IP 54 connection. The selected DHCPOFFER message contains a network host interface address (e.g., IP 54 address) in DHCP 66 yiaddr-field 126 (FIG. 6). A cable modem acknowledges the selected network host interface with DHCP 66 message sequence explained below.

After selecting and acknowledging a network host interface, CM 16 has discovered an IP 54 interface address available on CMTS 12 for completing a virtual IP 54 connection with data network 28. Acknowledging a network host interface is explained below. The virtual IP 54 connection allows IP 54 data from data network 28 to be sent to CMTS 12 which forwards the IP 54 packets to CM 16 on a downstream channel via cable network 14. CM 16 sends response IP 54 packets back to data network 28 via PSTN 22 and TRAC 24.

FIG. 8 is a block diagram illustrating a data-over-cable system 156 for the method illustrated in FIGS. 7A and 7B. Data-over-cable system 156 includes DHCP 66 proxies 158, DHCP 66 servers 160 and associated Network Host Interfaces 162 available on CMTS 12. Multiple DHCP 66 proxies 158, DHCP 66 servers 160 and network host interfaces 162 are illustrated as single boxes in FIG. 8. FIG. 8 also illustrates DHCP 66 proxies 158 separate from TRAC 24. In one embodiment of the present invention, TRAC 24 includes DHCP 66 proxy functionality and no separate DHCP 66 proxies 158 are used. In such an embodiment, TRAC 24 forwards DHCP 66 messages using DHCP 66 giaddr-field 130 to DHCP 66 servers 160 available on CMTS 12.

FIG. 9 is a block diagram illustrating a message flow 162 of method 140 (FIGS. 7A and 7B).

Message flow 162 includes DHCP proxies 158 and DHCP servers 160 illustrated in FIG. 8 Steps 142, 144, 146, 148, 150 and 154 of method 140 (FIGS. 7A and 7B) are illustrated in FIG. 9. In one embodiment of the present invention, DHCP proxies 158 are not separate entities, but are included in TRAC 24. In such an embodiment, DHCP proxy services are provided directly by TRAC 24.

Resolving Addresses for Network Host Interfaces

Since CM 16 receives multiple DHCPOFFER messages (Step 152 FIG. 7B) CM 16 resolves and acknowledges one offer from a selected network host interface. FIGS. 10A and 10B are a flow diagram illustrating a method 166 for resolving and acknowledging host addresses in a data-over-cable system. Method 166 includes a first network device that is connected to a first network with a downstream connection of a first connection type, and connected to a second network with an upstream connection of a second connection type. The first and second networks are connected to a third network with a third connection type. In one embodiment of the present invention, the first network device is CM 16, the first network is cable network 14, the second network is PSTN 22 and the third network is data network 28 (e.g., the Internet). The downstream connection is a cable television connection, the upstream connection is a telephony connection, and the third connection is an IP connection.

Turning to FIG. 10A, one or more first messages are received on the first network device from the first network on the downstream connection at step 168. The one or more first messages arc offers from one or more network host interfaces available on the first network to provide the first network device a connection to the third network. The first network device selects one of the network host interfaces using message fields in one of the one or more first messages at step 170. The first network device creates a second message with a second message type to accept the offered services from a selected network host interface at step 172. The second message includes a connection address for the first network in a first message field and an identifier to identify the selected network host interface in a second message field.

The first network device sends the second message over the upstream connection to the second network at step 174. The second network uses the first message field in the second message to forward the second message to the one or more network host interfaces available on first network at step 176.

A network host interface available on the first network identified in second message field in the second message from the first network device recognizes an identifier for the network host interface at 178 in FIG. 10B. The selected network host interface sends a third message with a third message type to the first network at step 180. The third message is an acknowledgment for the first network device that the selected network host interface received the second message from the first network device. The first network stores a connection address for the selected network interface in one or more tables on the first network at step 182. The first network will forward data from the third network to the first network device when it is received on the selected network host interface using the connection address in the one or more routing tables. The first network forwards the third message to the first network device on the downstream connection at step 184. The first network device receives the third message at step 186. The first network and the first network device have the necessary addresses for a virtual connection that allows data to be sent from the third network to a network host interface on the first network, and from the first network over the downstream connection to the first network device. Method 166 accomplishes resolving network interface hosts addresses from a cable modem in a data-over-cable with telephony return.

Method 166 of the present invention is used in data-over-cable system 10 with telephony return. However, the present invention is not limited to data-over-cable system 10 with telephony return and can be used in data-over-cable system 10 without telephony return by using an upstream cable channel instead of an upstream telephony channel.

FIGS. 11A and 11B are a flow diagram illustrating a method 188 for resolving 20 discovered host addresses in data-over-cable system 10 with telephony return. At step 190 in FIG. 11A, CM 16 receives one or more DHCPOFFER messages from one or more DHCP 66 servers associated with one or more network host interfaces (e.g., at step 168 in method 166). The one or more DHCPOFFER messages include DHCP 66 fields set as illustrated in Table 7 above. However, other field settings could also be used. At step 192, CM 16 selects one of the DHCPOFFER messages (see also, step 170 in method 166). At step 194, CM 16 creates a DHCP 66 request message ("DHCPREQUEST") message to request the services offered by a network host interface selected at step 192. The fields of the DHCP request message are set as illustrated in Table 8. However, other field settings may also be used.

                  TABLE 8                                                          ______________________________________                                         DHCP 66                                                                        Parameter   Description                                                        ______________________________________                                         OP 110      Set to BOOTREQUEST.                                                HTYPE 112   Set to network type (e.g., one for 10Mbps                                      Ethernet).                                                         HLEN 114    Set to network length (e.g., six for 10Mbps                                    Ethernet)                                                          HOPS 116    Set to zero.                                                       FLAGS 118   Set BROADCAST bit to zero.                                         CIADDR 124  If CM 16 has previously been assigned an IP                                    address, the IP address is placed in this field.                               If CM 16 has previously been assigned an IP                                    address by DHCP 66, and also has been                                          assigned an address via IPCP, CM 16 places                                     the DHCP 66 IP 54 address in this field.                           YIADDR 126  IP 54 address sent from the selected network                                   interface host in DCHPOFFER message                                GIADDR 130  CM 16 places the Downstream Channel IP 54                                      address 80 CMTS 12 obtained in TSI                                             message 76 on a cable downstream channel                                       in this field.                                                     CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                     in this field.                                                     SNAME 134   DHCP 66 server identifier for the selected                                     network interface host                                             ______________________________________                                    

The DHCPREQUEST message is used to "request" services from the selected IP 54 host interface available on CMTS 12 using a DHCP 66 server associated with the selected network host interface. DHCP 66 giaddr-field 130 (FIG. 6) includes the downstream channel IP address 80 for CMTS 12 obtained in TSI message 76 (e.g., the first message-field from step 172 of method 166). Putting the downstream channel IP address 80 obtained in TSI message 76 allows the DHCPREQUEST message to be forwarded by TRAC 24 to DCHP 66 servers associated with network host interfaces available on CMTS 12. DHCP 66 giaddr-field 126 contains an identifier (second message field, step 172 in method 166) DHCP 66 sname-field 134 contains a DHCP 66 server identifier associated with the selected network host interface.

If DHCP 66 giaddr-field 130 in a DHCP message from a DHCP 66 client is non-zero, a DHCP 66 server sends any return messages to a DHCP 66 server port on a DHCP 66 relaying agent (e.g., CMTS 12) whose address appears in DHCP 66 giaddr-field 130. If DHCP 66 giaddr-field 130 is zero, the DHCP 66 client is on the same subnet as the DHCP 66 server, and the DHCP 66 server sends any return messages to either the DHCP 66 client's network address, if that address was supplied in DHCP 66 ciaddr-field 124, or to the client's hardware address specified in DHCP 66 chaddr-field 132 or to the local subnet broadcast address.

Returning to FIG. 11A at step 196, CM 16 sends the DHCPREQUEST message on the upstream connection to TRAC 24 via PSTN 22. At step 198, a DHCP 66 layer on TRAC 24 broadcasts the DHCPREQUEST message on its local network leaving DHCP 66 giaddr-field 130 intact since it already contains a non-zero value. TRAC's 24 local network includes connections to one or more DHCP 66 proxies. The DHCP 66 proxies accept DHCP 66 messages originally from CM 16 destined for DHCP 66 servers associated with network host interfaces available on CMTS 12. In another embodiment of the present invention, TRAC 24 provides the DHCP 66 proxy functionality, and no separate DHCP 66 proxies are used.

The one or more DHCP 66 proxies on TRAC's 24 local network message forwards the DHCPOFFER to one or more of the DHCP 66 servers associated with network host interfaces (e.g., IP 54 interfaces) available on CMTS 12 at step 200 in FIG. 11B. Since DHCP 66 giaddr-field 130 in the DHCPDISCOVER message sent by CM 16 is already non-zero (i.e., contains the downstream IP address of CMTS 12), the DHCP 66 proxies leave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces (e.g., IP 54 interface) available on CMTS 12 receives the DHCPOFFER message at step 202. A selected DHCP 66 server recognizes a DHCP 66 server identifier in DHCP 66 sname-field 134 or the IP 54 address that was sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 from the DHCPREQUST message as being for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interface selected by CM 16 in the DHCPREQUEST message creates and sends a DCHP 66 acknowledgment message ("DHCPACK") to CMTS 12 at step 204. The DHCPACK message is sent with the message fields set as illustrated in Table 9. However, other field settings can also be used. DHCP 66 yiaddr-field again contains the IP 54 address for the selected network host interface available on CMTS 12 for receiving data packets from data network 28.

                  TABLE 9                                                          ______________________________________                                         DHCP 66 Parameter                                                                               Description                                                   ______________________________________                                         FLAGS 122        Set a BROADCAST bit to zero.                                  YIADDR 126       IP 54 address for the selected                                                 network host interface to allow                                                CM 16 to receive data from data                                                network 28.                                                   SIADDR 128       An IP 54 address for a TFTP 64                                                 server to download configuration                                               information for an interface host.                            CHADDR 132       MAC 44 address of CM 16.                                      SNAME 134        DHCP 66 server identifier                                                      associated with the selected                                                   network host interface.                                       FILE 136         A configuration file name for an                                               network interface host.                                       ______________________________________                                    

The selected DHCP 66 server sends the DHCACK message to the address specified in DHCP 66 giaddr-field 130 from the DHCPREQUEST message to CM 16 to verify the selected network host interface (e.g., IP 54 interface) will offer the requested service (e.g., IP 54 service).

At step 206, CMTS 12 receives the DHCPACK message from the selected DHCP 66 server associated with the selected network host interface IP 54 address(e.g., IP 54 interface). CMTS 12 examines DHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messages. DHCP 66 yiaddr-field 126 contains an IP 54 address for a network host IP 54 interface available on CMTS 12 and used for receiving IP 54 data packets from data network 28 for CM 16. DHCP 66 chaddr-field 132 contains the MAC 44 layer address for CM 16 on a downstream cable channel from CMTS 12 via cable network 14.

CMTS 12 updates an Address Resolution Protocol ("ARP") table and other routing tables on CMTS 12 to reflect the addresses in DHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 at step 208. As is known in the art, ARP allows a gateway such as CMTS 12 to forward any datagrams from a data network such as data network 28 it receives for hosts such as CM 16. ARP is defined in RFC-826, incorporated herein by reference.

CMTS 12 stores a pair of network address values in the ARP table, the IP 54 address of the selected network host interface from DHCP 66 yiaddr-field 126 and a Network Point of Attachment ("NPA") address. In an illustrative embodiment of the present invention, The NPA address is a MAC 44 layer address for CM 16 via a downstream cable channel. The IP/NPA address pair are stored in local routing tables with the IP/NPA addresses of hosts (e.g., CMs 16) that are attached to cable network 14.

At step 210, CMTS 12 sends the DHCPACK message to CM 16 via cable network 14. At step 212, CM 16 receives the DHCPACK message, and along with CMTS 12 has addresses for a virtual connection between data network 28 and CM 16. When data packets arrive on the IP 54 address for the selected host interface they are sent to CMTS 12 and CMTS 12 forwards them using a NPA (i.e., MAC 44 address) from the routing tables on a downstream channel via cable network 14 to CM 16.

If a BROADCAST bit in flags field 124 is set to one in the DHCPACK, CMTS 12 sends the DHCPACK messages to a broadcast IP 54 address (e.g., 255.255.255.255). DHCP 66 chaddr-field 132 is still used to determine that MAC layer address. If the BROADCAST bit in flags field 122 is set, CMTS 12 does not update the ARP table or offer routing tables based upon DHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when a broadcast message is sent.

FIG. 12 is a block diagram illustrating the message flow 214 of the method 188 illustrated in FIGS. 11A and 11B. Message flow 214 includes DHCP proxies 158 and DHCP servers 160 illustrated in FIG. 8. Method steps 194, 196, 198, 204, 208, 210 and 212 of method 188 (FIGS. 11A and 11B) are illustrated in FIG. 12. In one embodiment of the present invention, DHCP proxies 158 are not separate entities, but are included in TRAC 24. In such an embodiment, DHCP proxy services are provided directly by TRAC 24.

After method 188, CMTS 12 has a valid IP/MAC address pair in one or more address routing tables including an ARP table to forward IP 54 data packets from data network 28 to CM 16, thereby creating a virtual IP 54 data path to/from CM 16 as was illustrated in method 92 (FIG. 5) and Table 3. CM 16 has necessary parameters to proceed to the next phase of initialization, a download of a configuration file via TFTP 64. Once CM 16 has received the configuration file and has been initialized, it registers with CMTS 12 and is ready to receive data from data network 14.

In the event that CM 16 is not compatible with the configuration of the network host interface received in the DHCPACK message, CM 16 may generate a DHCP 66 decline message ("DHCPDECLINE") and transmit it to TRAC 24 via PSTN 22. A DHCP 66 layer in TRAC 24 forwards the DHCPDECLINE message to CMTS 12. Upon seeing a DHCPDECLINE message, CMTS 12 flushes its ARP tables and routing tables to remove the now invalid IP/MAC pairing. If an IP 54 address for a network host interface is returned that is different from the IP 54 address sent by CM 16 in the DCHCPREQUEST message, CM 16 uses the IP 54 address it receives in the DHCPACK message as the IP 54 address of the selected network host interface for receiving data from data network 28.

The present invention is described with respect to, but is not limited to a data-over-cable-system with telephony return. Method 188 can also be used with a cable modem that has a two-way connection (i.e., upstream and downstream) to cable network 14 and CMTS 12. In a data-over-cable-system without telephony return, CM 16 would broadcast the DHCPREQUEST message to one or more DHCP 66 servers associated with one or more network host interfaces available on CMTS 12 using an upstream connection on data network 14 including the IP 54 address of CMTS 12 in DHCP 66 giaddr-field 130. Method 188 accomplishes resolving addresses for network interface hosts from a cable modem in a data-over-cable with or without telephony return, and without extensions to the existing DHCP protocol.

CPE Initialization in a Data-over-cable System

CPE 18 also uses DHCP 66 to generate requests to obtain IP 54 addresses to allow CPE 18 to also receive data from data network 28 via CM 16. In an illustrative embodiment of the present invention, CM 16 functions as a standard BOOTP relay agent/DHCP Proxy 158 to facilitate CPE's 18 access to DHCP 66 server 160. FIGS. 13A and 13B are a flow diagram illustrating a method 216 for obtaining addresses for customer premise equipment. CM 16 and CMTS 12 use information from method 214 to construct IP 54 routing and ARP table entries for network host interfaces 162 providing data to CMCI 20 and to CPE 18.

Method 216 in FIGS. 13A and 13B includes a data-over-cable system with telephony return and first network device with a second network device for connecting the first network device to a first network with a downstream connection of a first connection type, and for connecting to a second network with an upstream connection of a second connection type. The first and second networks are connected to a third network with a third connection type.

In one embodiment of the present invention, data-over-cable system with telephony return is data-over-cable system 10 with the first network device CPE 18 and the second network device CM 16. The first network is cable television network 14, the downstream connection is a cable television connection, the second network is PSTN 22, the upstream connection is a telephony connection, the third network is data network 28 (e.g., the Internet or an intranet) and the third type of connection is an IP 54 connection. However, the present invention is not limited to the network components described and other network components may also be used. Method 216 allows CPE 18 to determine an IP 54 network host interface address available on CMTS 12 to receive IP 54 data packets from data network 54, thereby establishing a virtual IP 54 connection with data network 28 via CM 16.

Returning to FIG. 13A at step 218, a first message of a first type (e.g., a DHCP 66 discover message) with a first message field for a first connection is created on the first network device. The first message is used to discover a network host interface address on the first network to allow a virtual connection to the third network.

At step 220, the first network device sends the first message to the second network device. The second network device checks the first message field at step 222. If the first message field is zero, the second network device puts its own connection address into the first message field at step 224. The second network device connection address allows the messages from network host interfaces on the first network to return messages to the second network device attached to the first network device. If the first message field is non-zero, the second network device does not alter the first message field since there could be a relay agent attached to the first network device that may set the first connection address field.

At step 226, the second network device forwards the first message to a connection address over the upstream connection to the second network. In one embodiment of the present invention, the connection address is an IP broadcast address (e.g., 255.255.255.255). However, other connection addresses can also be used.

The second network uses the first connection address in the first message field in the first message to forward the first message to one or more network host interfaces (e.g., IP 54 network host interfaces) available on first network at step 228. One or more network host interfaces available on the first network that can provide the services requested in first message send a second message with a second message type with a second connection address in a second message field to the first network at step 230 in FIG. 13B. The second connection address allows the first network device to receive data packets from the third network via a network host interface on the first network. The first network forwards the one or more second messages on the downstream connection to the second network device at step 232. The second network device forwards the one or more second messages to the first network device at step 234. The first network device selects one of the one or more network host interfaces on the first network using the one or more second messages at step 236. This allows a virtual connection to be established between the third network and the first network device via the selected network host interface on the first network and the second network device.

FIGS. 14A and 14B are a flow diagram illustrating a method 240 for resolving addresses for the network host interface selected by a first network device to create a virtual connection to the third network. Turning to FIG. 14A, at step 240 one or more second messages are received with a second message type on the first network device from the second network device from the first network on a downstream connection at step 242. The one or more second messages are offers from one or more protocol servers associated with one or more network host interfaces available on the first network to provide the first network device a connection to the third network. The first network device selects one of the network host interfaces using one of the one or more second messages at step 244. The first network device creates a third message with a third message type to accept the offered services from the selected network host interface at step 246. The third message includes a connection address for the first network in a first message field and an identifier to identify the selected network host interface in a second message field. At step 248, first network device equipment sends the third message to the second network device.

The second network device sends the third message over the upstream connection to the second network at step 250. The second network uses the first message field in the third message to forward the third message to the one or more network host interfaces available on first network at step 252.

A network host interface available on the first network identified in second message field in the third message from the first network device recognizes an identifier for the selected network host interface at step 254 in FIG. 14B. The selected network host interface sends a fourth message with a fourth message type to the first network at step 256. The fourth message is an acknowledgment for the first network device that the selected network host interface received the third message. The fourth message includes a second connection address in a third message field. The second connection address is a connection address for the selected network host interface. The first network stores the connection address for the selected network interface from the third message in one or more routing tables (e.g., an ARP table) on the first network at step 258. The first network will forward data from the third network to the first network device via the second network device when it is received on the selected network host interface using the connection address from the third message field. The first network forwards the fourth message to the second network device on the downstream connection at step 260. The second network device receives the fourth message and stores the connection address from the third message field for the selected network interface in one or more routing tables on the second network device at step 262. The connection address for the selected network interface allows the second network device to forward data from the third network sent by the selected network interface to the customer premise equipment.

At step 264, the second network device forward the fourth message to the first network device. At step 266, the first network device establishes a virtual connection between the third network and the first network device.

After step 266, the first network, the second network device and the first network device have the necessary connection addresses for a virtual connection that allows data to be sent from the third network to a network host interface on the first network, and from the first network over the downstream connection to the second network and then to the first network device. In one embodiment of the present invention, method 240 accomplishes resolving network interface hosts addresses from customer premise equipment with a cable modem in a data-over-cable with telephony return without extensions to the existing DHCP protocol.

Methods 216 and 240 of the present invention are used in data-over-cable system 10 with telephony return with CM 16 and CPE 18. However, the present invention is not limited to data-over-cable system 10 with telephony return and can be used in data-over-cable system 10 without telephony return by using an upstream cable channel instead of an upstream telephony channel.

FIGS. 15A and 15B are a flow diagram illustrating a method 268 for addressing network host interfaces from CPE 18. At step 270 in FIG. 15A, CPE 18 generates a DHCPDISCOVER message broadcasts the DHCPDISCOVER message on its local network with the fields set as illustrated in Table 6 above with addresses for CPE 18 instead of CM 16. However, more or fewer field could also be set. CM 16 receives the DHCPDISCOVER as a standard BOOTP relay agent at step 272. The DHCP DISCOVER message has a MAC 44 layer address for CPE 18 in DHCP 66 chaddr-field 132, which CM 16 stores in one or more routing tables. As a BOOTP relay agent, the CM 16 checks the DHCP 66 giaddr-field 130 (FIG. 6) at step 274. If DHCP 66 giaddr-field 130 is set to zero, CM 16 put its IP 54 address into DHCP 66 giaddr-field 130 at step 276.

If DHCP 66 giaddr-field 130 is non-zero, CM 16 does not alter DHCP 66 giaddr-field 130 since there could be another BOOTP relay agent attached to CPE 18 which may have already set DHCP 66 giaddr-field 130. Any BOOTP relay agent attached to CPE 18 would have also have acquired its IP 54 address from using a DCHP 66 discovery process (e.g., FIG. 12).

Returning to FIG. 15A, at step 278, CM 16 broadcasts the DHCPDISCOVER message to a broadcast address via PSTN 22 to TRAC 24. In one embodiment of the present invention, the broadcast address is an IP 54 broadcast address (e.g., 255.255.255.255). At step 280, one or more DHCP 66 proxies 158 associated with TRAC 24, recognize the DHCPDISOVER message, and forward it to one or more DHCP 66 servers 160 associated with one or more network host interfaces 162 available on CMTS 12. Since DHCP 66 giaddr-field 130 is already non-zero, the DHCP proxies leave DHCP 66 giaddr-field 130 intact. In another embodiment of the present invention, TRAC 24 includes DCHP 66 proxy 158 functionality and no separate DHCP 66 proxies 158 are used.

At step 282 in FIG. 15B, the one or more DHCP servers 160 receive the DHCPDISCOVER message from one or more DHCP proxies, and generate one or more DHCPOFFER messages to offer connection services for one or more network host interfaces 162 available on CMTS 12 with the fields set as illustrated in Table 7. The one or more DHCP servers 160 send the one or more DHCPOFFER messages to the address specified in DHCP 66 giaddr-field 130 (e.g., CM 16 or a BOOTP relay agent on CPE 18), which is an IP 54 address already contained in an ARP or other routing table in CMTS 12. Since CMTS 12 also functions as a relay agent for the one or more DHCP servers 160, the one or more DHCPOFFER messages are received on CMTS 12 at step 284.

CMTS 12 examines DHCP 66 yiaddr-field 126 and DHCP 66 giaddr-field 130 in the DHCPOFFER messages, and sends the DHCPOFFER messages down cable network 14 to IP 54 address specified in the giaddr-field 130. The MAC 44 address for CM 16 is obtained through a look-up of the hardware address associated with DHCP 66 chaddr-field 130. If the BROADCAST bit in DHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPOFFER message to a broadcast IP 54 address (e.g., 255.255.255.255), instead of the address specified in DHCP 66 yiaddr-field 126 CMTS 12 does not update its ARP or other routing tables based upon the broadcast DCHP 66 yiaddr-field 126 DHCP 66 chaddr-field 132 address pair.

Returning to FIG. 15B, CM 16 receives the one or more DHCPOFFER messages and forwards them to CPE 18 at step 286. CM 16 uses the MAC 44 address specified determined by DHCP 66 chaddr-field 132 look-up in its routing tables to find the address of CPE 18 even if the BROADCAST bit in DHCP 66 flags-field 122 is set. At step 290, CPE 18 receives the one or more DHCPOFFER messages from CM 16. At step 292, CPE 18 selects one of the DHCPOFFER messages to allow a virtual connection to be established between data network 28 and CPE 18. Method 266 accomplishes addressing network interface hosts from CPE 18 in data-over-cable system 10 without extensions to the existing DHCP protocol.

FIGS. 16A and 16B are a flow diagram illustrating a method 294 for resolving network host interfaces from CPE 18. At step 296, CPE 18 receives the one or more DHCPOFFER messages from one or more DHCP 66 servers associated with one or more network host interface available on CMTS 12. At step 298, CPE 18 chooses one offer of services from a selected network host interface. At step 300, CPE 18 generates a DHCPREQUEST message with the fields set as illustrated in Table 8 above with addresses for CPE 18 instead of CM 16. However, more or fewer fields could also be set. At step 302, CPE 18 sends the DHCPREQUEST message to CM 16. At step 304, CM 16 forwards the message to TRAC 24 via PSTN 22.

At step 306, a DHCP 66 layer on TRAC 24 broadcasts the DHCPREQUEST message on its local network leaving DHCP 66 giaddr-field 130 intact since it already contains a non-zero value. TRAC's 24 local network includes connections to one or more DHCP 66 proxies. The DHCP 66 proxies accept DHCP 66 messages originally from CPE 18 destined for DHCP 66 servers associated with network host interfaces available on CMTS 12. In another embodiment of the present invention, TRAC 24 provides the DHCP 66 proxy functionality, and no separate DHCP 66 proxies are used.

One or more DHCP 66 proxies on TRAC's 24 local network recognize the DHCPOFFER message and forward it to one or more of the DHCP 66 servers associated with network host interfaces (e.g., IP 54 interfaces) available on CMTS 12 at step 308 in FIG. 16B. Since DHCP 66 giaddr-field 130 in the DHCPDISCOVER message sent by CPE 18 is already non-zero, the DHCP 66 proxies leave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces (e.g., IP 54 interface) available on CMTS 12 receive the DHCPOFFER message at step 310. A selected DHCP 66 server recognizes a DHCP 66 server identifier in DHCP 66 sname-field 134 or the IP 54 address that was sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 from the DHCPREQUST message for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interface selected by CPE 18 in the DHCPREQUEST message creates and sends a DCHP acknowledgment message ("DHCPACK") to CMTS 12 at step 312 using the DHCP 66 giaddr-field 130. The DHCPACK message is sent with the message fields set as illustrated in Table 9. However, other field settings can also be used. DHCP 66 yiaddr-field contains the IP 54 address for the selected network host interface available on CMTS 12 for receiving data packets from data network 28 for CPE 18.

At step 314, CMTS 12 receives the DHCPACK message. CMTS 12 examines the DHCP 66 giaddr-field 130 and looks up that IP address in its ARP table for an associated MAC 44 address. This is a MAC 44 address for CM 16, which sent the DHCPREQUEST message from CPE 18. CMTS 12 uses the MAC 44 address associated with the DHCP 66 giaddr-field 130 and the DHCP 66 yiaddr-field 126 to update its routing and ARP tables reflecting this address pairing at step 316. At step 318, CMTS 12 sends the DHCPACK message on a downstream channel on cable network 14 to the IP 54 and MAC 44 addresses, respectively (i.e., to CM 16). If the BROADCAST bit in the DHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPACK message to a broadcast IP 54 address (e.g., 255.255.255.255), instead of the address specified in the DHCP 66 yiaddr-field 126 CMTS 12 uses the MAC 44 address associated with the DHCP 66 chaddr-field 130 even if the BROADCAST bit is set.

CM 16 receives the DHCPACK message. It examines the DHCP 66 yiaddr-field 126 and chaddr-field 132, and updates its routing table and an ARP routing table to reflect the address pairing at step 320. At step 322, CM 16 sends the DHCPACK message to CPE 18 via CMCI 20 at IP 54 and MAC 44 addresses respectively from its routing tables. If the BROADCAST bit in the DHCP 66 flags-field 122 is set to one, CM 16 sends the downstream packet to a broadcast IP 54 address (e.g., 255.255.255.255), instead of the address specified in DHCP 66 yiaddr-field 126. CM 16 uses the MAC 44 address specified in DHCP 66 chaddr-field 132 even if the BROADCAST bit is set to located CPE 18. At step 324, CPE 18 receives the DHCPACK from CM 16 and has established a virtual connection to data network 28.

In the event that CPE 18 is not compatible with the configuration received in the DHCPACK message, CPE 18 may generate a DHCP 66 decline ("DHCPDECLINE") message and send it to CM 16. CM 16 will transmit the DHCPDECLINE message up the PPP 50 link via PSTN 22 to TRAC 24. On seeing a DHCPDECLINE message TRAC 24 sends a unicast copy of the message to CMTS 12. CM 16 and CMTS 12 examine the DHCP 66 yiaddr-field 126 and giaddr-field 130, and update their routing and ARP tables to flush any invalid pairings.

Upon completion of methods 266 and 292, CM 16 CMTS 12 have valid IP/MAC address pairings in their routing and ARP tables. These tables store the same set of IP 54 addresses, but does not associate them with the same MAC 44 addresses. This is because CMTS 12 resolves all CPE 18 IP 54 addresses to the MAC 44 address of a corresponding CM 16. The CMs 16, on other hand, are able to address the respective MAC 44 addresses of their CPEs 18. This also allows DHCP 66 clients associated with CPE 18 to function normally since the addressing that is done in CM 16 and CMTS 12 is transparent to CPE 18 hosts.

FIG. 17 is a block diagram illustrating a message flow 326 for methods 268 and 294 in FIGS. 15A, 15B, and 16A and 16B. Message flow 326 illustrates a message flow for methods 268 and 294, for a data-over-cable system with and without telephony return. In another embodiment of the present invention, CM 16 forwards requests from CPE 18 via an upstream connection on cable network 14 to DHCP servers 160 associated with one or more network host interfaces available on CMTS 12.

Method 268 and 294 accomplishes resolving addresses for network interface hosts from customer premise equipment in a data-over-cable with or without telephony return without extensions to the existing DHCP protocol. Methods 268 and 294 of the present invention are used in data-over-cable system 10 with telephony return. However, the present invention is not limited to data-over-cable system 10 with telephony return and can be used in data-over-cable system 10 without telephony return by using an upstream cable channel instead of an upstream telephony channel. 

We claim:
 1. In a data-over-cable system with a plurality of network devices connected a first network with a downstream connection of a first connection type and connected to a second network with an upstream connection of a second connection type, wherein the first and second networks are connected to a third network with a third connection type, a method of addressing network host interfaces, the method comprising the following steps:receiving on a first network device on the downstream connection from the first network, a plurality of first messages, wherein the plurality of first messages include offers from a plurality of network host interfaces available on the first network to connect the first network device to the third network; selecting on the first network device a network interface host available on the first network using the plurality of first messages; creating on the first network device a second message with a second message type, the second message including a first connection address in a first message field for communicating with the first network and a network host interface identifier in a second message field for the selected network host interface; sending the second message from the first network device on the upstream connection to the second network; routing the second message from the second network to a plurality of network host interfaces available on the first network using the first connection address from the first field in the first message; recognizing from the selected network host interface available on the first network a network host identifier in the second message field in the second message for the selected network host interface; sending a third message with a third message type from the selected network host interface to the first network, wherein the third message acknowledges the second message sent by the first network device and includes a second connection address to the third network for the selected network host interface; storing the second network connection address from the third message in one or more routing tables in the first network; and forwarding the third message from the first network over the downstream connection to the first network device; receiving the third message on the first network device, thereby establishing a virtual connection from the third network to the first network device, wherein the first network and the first network device have a network connection address for the selected network host interface that allows data to be sent over the virtual connection from the third network to the network host interface on the first network, and from the first network to the first network device over the downstream connection.
 2. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim
 1. 3. The method of claim 1 wherein the first network device is a cable modem, the first network is a cable television network, the second network is a public-switched telephone network and the third network is a data network.
 4. The method of claim 3 wherein the data network is any of the Internet or intranet.
 5. The method of claim 1 wherein the downstream connection is a cable television connection, the upstream connection is a serial line connection and the third connection type is an Internet Protocol connection.
 6. The method of claim 1 wherein the first network and the second network are a cable television network and the third network is a data network.
 7. The method of claim 6 wherein the downstream connection is a cable television connection, the upstream connection is a cable television connection and the third connection type is an Internet Protocol connection.
 8. The method of claim 1 wherein the first message is a Dynamic Host Configuration Protocol offer message, the second message is a Dynamic Host Configuration Protocol request message, the first message field is a Dynamic Host Configuration Protocol message giaddr-field, and the third message is a Dynamic Host Configuration Protocol acknowledgment message.
 9. The method of claim 1 wherein the virtual connection further includes sending data from the cable modem back to the third network over the upstream connection to the second network.
 10. The method of claim 1 wherein the first connection address and the second connection address are Internet Protocol addresses.
 11. The method of claim 1 wherein the step of sending the second message includes sending the second message to a telephony remote access concentrator on the second network.
 12. The method of claim 1 wherein the step of sending a third message includes sending the third message to a cable modem termination system on the first network.
 13. The method of claim 1 wherein the step of sending the second message includes forwarding the second message to a plurality of network host servers associated with the plurality of network host interfaces available on the first network.
 14. The method of claim 13 wherein the plurality of network host servers includes a plurality of Dynamic Host Configuration Protocol servers.
 15. In a data-over-cable system with a plurality of network devices connected to a first network device on first network with a downstream connection of a first connection type, and connected to a second network device on a second network with an upstream connection of a second connection type, wherein the first and second network devices are connected to a third network with a third connection type, a method of discovering network interfaces, the method comprising the following steps:creating on a third network device first message with a first message type, the first message including a first connection address in a first message field for communicating with the first network and a network host interface identifier in a second message field for the selected network host interface; sending the first message from the third network device on the upstream connection to the second network device on the second network; broadcasting the first message from the second network device to a plurality of protocol servers associated with network host interfaces available on the first network using the first connection address from the first field in the first message; recognizing from a selected protocol server associated with a selected network host interface available on the first network that the first message is for the selected network host interface; sending a second message with a second message type from the selected protocol server to the first network device, wherein the second message acknowledges the first message sent by the third network device and includes a second connection address to the third network for the selected network host interface; storing the second network connection address from the second message in one or more routing tables on the first network device on the first network; and forwarding the second message from the first network device on the first network over the downstream connection to the third network device; receiving the second message on the third network device, wherein the first network device and the third network device have a network connection address for the selected network host interface that allows data to be sent over a virtual connection from the third network to the network host interface available on the first network device, and from the first network device to the third network device.
 16. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim
 15. 17. The method of claim 15 wherein the step of broadcasting the first message from the second network device includes broadcasting the first message to a plurality of protocol proxies available on the second network device.
 18. The method of claim 17 wherein the plurality of protocol proxies include a plurality of Dynamic Host Configuration Protocol proxies.
 19. The method of claim 15 wherein the plurality of protocol servers include a plurality of Dynamic Host Configuration Protocol servers.
 20. The method of claim 15 wherein the first network device is a cable modem termination system and the second network device is a telephony return access concentrator and the third network device is a cable modem.
 21. The method of claim 15 wherein the first message is a Dynamic Host Configuration Protocol request message and the second message is a Dynamic Host Configuration Protocol acknowledgment message.
 22. The method of claim 15 wherein the first message field is a Dynamic Host Configuration Protocol message giaddr-field.
 23. The method of claim 15 wherein the first network is a cable television network, the second network is a public-switched telephone network and the third network is a data network.
 24. The method of claim 15 wherein the data network is any of the Internet or intranet.
 25. A data-over-cable system comprising:plurality of Dynamic Host Configuration Protocol proxies available on a telephony remote access concentrator, for forwarding requests to a plurality of Dynamic Host Configuration Protocol servers; plurality of Dynamic Host Configuration Protocol servers available on a cable modem termination system, for forwarding requests to network host interfaces; plurality of network host interfaces available on the cable modem termination system, for providing interfaces to a data network for a cable modem via the cable modem termination system; and virtual data connection, for connecting the cable modem to the data network, wherein the virtual data connection includes sending data from the data network to the cable modem through the cable modem termination system and the downstream connection on the cable television network, and sending data to the data network from the cable modem through the telephony return access concentrator and the upstream connection on the public switched telephone network.
 26. In a data-over-cable system with a cable modem connected to a cable modem termination system on cable television network with a downstream connection, and connected to a telephony remote access concentrator on a public switched telephone network with an upstream connection, wherein the cable modem termination system and telephony remote access concentrator are connected to a data network, a method of discovering network interfaces, the method comprising the following steps:creating on the cable modem a Dynamic Host Configuration Protocol request message, including a first connection address in a first message field for communicating with the cable modem termination system and a network host interface identifier in a second message field for a selected network host interface; sending the Dynamic Host Configuration Protocol request message from the cable modem on the upstream connection to telephony remote access concentrator via the public switched telephone network; broadcasting the Dynamic Host Configuration Protocol request message from the telephony remote access concentrator to a plurality of Dynamic Host Configuration Protocol proxies using the first connection address from the first field in the first message; forwarding the Dynamic Host Configuration Protocol request message from the plurality of Dynamic Host Configuration Protocol proxies to a plurality of Dynamic Host Configuration Protocol servers associated with a plurality of network host interfaces available on the cable modem termination system; recognizing from a selected Dynamic Host Configuration Protocol server associated with a selected network host interface available on the cable modem termination system that the Dynamic Host Configuration Protocol request message is for the selected network host interface; sending a Dynamic Host Configuration Protocol acknowledgment message from the selected network host interface to the cable modem termination system, wherein the Dynamic Host Configuration Protocol acknowledge message acknowledges the Dynamic Host Configuration Protocol request sent by the cable modem and includes a second connection address for the selected network host interface to the data network; storing the second network connection address from the Dynamic Host Configuration Protocol message in one or more routing tables on the cable modem termination system; and forwarding the Dynamic Host Configuration Protocol acknowledge message from the cable modem termination system over the downstream connection to the cable modem; receiving the Dynamic Host Configuration Protocol acknowledge message on the cable modem, wherein the cable modem termination system and the cable modem have a network connection address for the selected network host interface that allows data to be sent over a virtual connection from the data network to the network host interface available on the cable modem termination system, and from the cable modem termination system to the cable modem on the downstream connection.
 27. A computer readable medium having stored therein instructions for causing a central processing unit to execute the method of claim
 26. 